Looking in the brain
Imaging techniques help researchers get into the heads of people with addiction
The brains of laboratory animals can be analysed to yield extremely precise data – down to the firing of single neurons – while they are taking in drugs.
Looking at the reward system in human brains has to be less direct, but modern imaging technology shows things going on in there that fit with the animal findings.
The most often-used technique is functional magnetic resonance imaging (fMRI). This detects the difference in the magnetic resonance (the ability of molecules to absorb certain radiation frequencies) of haemoglobin and oxyhaemoglobin, so it can tell if the blood has oxygen or not. That in turn shows detailed changes in the blood flow around the brain – areas with increased blood flow are using more oxygen and respiring faster, so are more active. These more active areas show up as brighter on the screen.
fMRI can show how brain activity changes in real time. For instance, the brain’s reward regions have been found to ‘light up’ under the influence of cocaine injections, so they are more active at that point. As the cocaine wears off the blood flow decreases and the reward regions on the screen are less bright.
Another technique, positron emission tomography (PET), can probe more specific aspects of brain biochemistry. A small amount of radioactive material is given to the person via injection or inhalation. These radioactive molecules (often oxygen, or carbon incorporated in glucose) move to the brain regions that are most active. The molecules then break down, resulting in the release of a gamma ray, which is detected by special imaging machines. This then shows which areas of the brain are more active.
Imaging studies also confirm that the brain regions that are activated when cocaine addicts are offered a hit, such as the nucleus accumbens, also react when addicts are shown drug-related images such as white lines on a mirror. Other studies have shown similar results with compulsive gamblers looking at photos of slot machines.
Being able to study and understand how the brain is affected by substance abuse is important for understanding how addiction occurs at the neurological level, and may help with treating these addictions.Lead image:
Mark Lythgoe and Chloe Hutton/Wellcome Images